Conventionally, a manufacturing process of a semiconductor device uses a CVD apparatus that forms a film by a CVD (Chemical Vapor Deposition) method. The CVD apparatus includes a diffusion plate that straightens a process gas for film deposition in a chamber. The diffusion plate has a plurality of through holes allowing the process gas to pass therethrough toward a wafer. The position and the opening area of each through hole and the number of the through holes are designed to provide a desired distribution of a film thickness in a plane of the wafer (hereinafter, also “in-plane distribution”).
In recent years, a lamination deposition process has been developed in which plural types of films are laminated in the same chamber. In a case of applying the diffusion plate to the lamination deposition process, the through holes can be designed to provide a desired in-plane distribution of a film thickness for one type of film. However, an in-plane distribution of a film thickness for other types of films is degraded under such specialized design of through holes for the one type of film.